The Posse Comitatus organization was an extreme right-wingtax resistance movement active in the U.S. in the 1970s and early 1980s. It was strongest in the rural Midwestern states where a farm foreclosure crisis gave them an appealing recruiting target. Less an organized group than a decentralized movement, they generally held that the only legitimate form of government was at the county level (posse comitatus is Latin for "power of the county") and did not recognize the state or federal government. They believed the county sheriff was therefore the head of state, and the unorganized militia of the county (themselves) was the sheriff's enforcement arm under their admittedly bizarre reading of common law. (See: pseudolaw) It is not documented exactly how Posse Comitatus activists felt that this would work in areas of the country with weak or non-existent county governments (such as New England or Alaska), or in New York City, where the governments of five counties (the Five Boroughs) have been completely subsumed by the city government.

The movement was also closely tied to Christian Identity beliefs and anti-Semitism. One of its leaders, James Wickstrom, is an Identity church pastor who believes in the serpent seed doctrine and often preaches on the subject, "Communism is Jewish". Other founders included Henry Lamont Beach, a former member of the pro-Axis "Silver Shirts" (a group active in the U.S. just before World War II), and William Potter Gale, an anti-Semite who is ironically of part Jewish ancestry himself.

Gordon Kahl of Medina, North Dakota was probably their best known member, who died in a 1983 shootout with law enforcement in Arkansas while fleeing federal tax charges and a gunfight during an earlier botched arrest attempt in Medina, North Dakota.

While Posse Comitatus is not active in any significant sense, its ideology led to the sovereign citizen movement as well as the closely related militia movement. The anonymous propaganda tract known as the Citizen's Rule Book is also believed to have been written by either members or sympathizers of PC due to its ideological slant.

Following the Haiti earthquake of January 2010, Wickstrom's Comitatus blog headlined with: "PRAISE YAHWEH FOR DESTROYING THESE BUTCHERS OF WHITES & VODOO CREATURES!!".[1]